A region of tissue plasminogen activator that affects plasminogen activation differentially with various fibrin(ogen)-related stimulators

• Published in: Biochemistry (Easton) Vol. 31; no. 2; pp. 419 - 422
• Main Authors: Eastman, Donna, Wurm, Florian M, Van Reis, Robert, Higgins, Deborah L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21.01.1992
• Subjects: activation; Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Catalysis; characterization; coagulation factors; Enzyme Activation; Enzymes and enzyme inhibitors; Fibrin Fibrinogen Degradation Products; Fibrinogen - genetics; Fibrinogen - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Hydrolases; Kidney; Kinetics; man; Molecular Sequence Data; Mutagenesis, Site-Directed; plasmin; Plasminogen - metabolism; plasminogen activator; proteins; Recombinant Proteins - genetics; Recombinant Proteins - pharmacology; requirements; Tissue Plasminogen Activator - chemistry; Tissue Plasminogen Activator - genetics; Tissue Plasminogen Activator - pharmacology; Sequence specificity; Enzyme; Site directed mutagenesis; Plasminogen activator; Activation; Kinetics; Plasminogen; Recombinant protein; Comparative study
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00117a016

The dissolution of blood clots by plasmin is normally initiated in vivo by the activation of plasminogen to plasmin through the activity of tissue plasminogen activator (t-PA). The rate of plasminogen activation can be stimulated several orders of magnitude by the presence of fibrin-related proteins. Here we describe the kinetic analysis of both recombinant human t-PA (wild-type) and a t-PA variant produced by site-directed mutagenesis in which the original sequence from amino acids 296 to 299, KHRR, has been altered to AAAA. This tetra-alanine variant form of t-PA, K296A/H297A/R298A/R299A t-PA, we refer to as "KHRR" t-PA here. The plasminogen activating kinetics of wild-type t-PA (Activase alteplase) showed a catalytic efficiency which changed over 100-fold dependent on the stimulator in the assay. The lowest rate was in the absence of a stimulator. The following stimulators showed increasing ability to accelerate the catalytic efficiency of the reaction: fibrinogen, fragments of fibrinogen obtained by digestion with plasmin, fibrin, and slightly degraded fibrin. This increase in efficiency was driven primarily by decreases in the Michaelis constant (KM) of the reaction, whereas the catalytic rate constant (kcat) of the reaction did not change significantly. The "KHRR" variant of t-PA displayed novel kinetics with all stimulators tested. In the absence of a stimulator or with the poorer stimulators (fibrinogen and fibrinogen fragments), the KM values of the reaction with Activase alteplase and "KHRR" t-PA were similar. The kcat however, was lower with "KHRR" t-PA than with wild-type t-PA.